Chapter 2 - Software Processes Lecture 1 PDF

Chapter 2 – Software Processes Lecture 1 Chapter 2 Software Processes 1 Topics covered  Software process models  Process activities  Coping with change  The Rational Unified Process  An example of a modern software process. Ch...

Chapter 2 – Software Processes Lecture 1 Chapter 2 Software Processes 1 Topics covered  Software process models  Process activities  Coping with change  The Rational Unified Process  An example of a modern software process. Chapter 2 Software Processes 2 The software process Chapter 2 Software Processes 3 Software process descriptions  When we describe and discuss processes, we usually talk about the activities in these processes such as specifying a data model, designing a user interface, etc. and the ordering of these activities.  Process descriptions may also include:  Products, which are the outcomes of a process activity;  Roles, which reflect the responsibilities of the people involved in the process;  Pre- and post-conditions, which are statements that are true before and after a process activity has been enacted or a product produced. Chapter 2 Software Processes 4 Plan-driven and agile processes  Plan-driven processes are processes where all of the process activities are planned in advance and progress is measured against this plan.  In agile processes, planning is incremental and it is easier to change the process to reflect changing customer requirements.  In practice, most practical processes include elements of both plan-driven and agile approaches.  There are no right or wrong software processes. Chapter 2 Software Processes 5 Software process models  The waterfall model  Plan-driven model. Takes the fundamental process activities of specification, development, validation and evolution and represents them as a separate process phases such as requirements specification, software design, implementation, testing and so on.  Incremental development  Specification, development and validation are interleaved. May be plan-driven or agile.  Reuse-oriented software engineering  The system is assembled from existing components. May be plan-driven or agile.  In practice, most large systems are developed using a process that incorporates elements from all of these models. Chapter 2 Software Processes 6 The waterfall model Chapter 2 Software Processes 7 Waterfall model phases Chapter 2 Software Processes 8 Waterfall model problems Chapter 2 Software Processes 9 Incremental development Chapter 2 Software Processes 10 Incremental development benefits Chapter 2 Software Processes 11 Incremental development problems  The process is not visible.  Managers need regular deliverables to measure progress. If systems are developed quickly, it is not cost-effective to produce documents that reflect every version of the system.  System structure tends to degrade as new increments are added.  Unless time and money is spent on refactoring to improve the software, regular change tends to corrupt its structure. Incorporating further software changes becomes increasingly difficult and costly. Chapter 2 Software Processes 12 Reuse-oriented software engineering Chapter 2 Software Processes 13 Reuse-oriented software engineering Chapter 2 Software Processes 14 Types of software component  Web services that are developed according to service standards and which are available for remote invocation.  Collections of objects that are developed as a package to be integrated with a component framework such as.NET or J2EE.  Stand-alone software systems (COTS) that are configured for use in a particular environment. Chapter 2 Software Processes 15 Process activities  Real software processes are inter-leaved sequences of technical, collaborative and managerial activities with the overall goal of specifying, designing, implementing and testing a software system.  The four basic process activities of specification, development, validation and evolution are organized differently in different development processes. In the waterfall model, they are organized in sequence, whereas in incremental development they are inter- leaved. Chapter 2 Software Processes 16 Software specification  The process of establishing what services are required and the constraints on the system’s operation and development.  Requirements engineering process  Feasibility study Is it technically and financially feasible to build the system?  Requirements elicitation and analysis What do the system stakeholders require or expect from the system?  Requirements specification Defining the requirements in detail  Requirements validation Checking the validity of the requirements Chapter 2 Software Processes 17 The requirements engineering process Chapter 2 Software Processes 18 Software design and implementation Chapter 2 Software Processes 19 A general model of the design process Chapter 2 Software Processes 20 Design activities  Architectural design, where you identify the overall structure of the system, the principal components (sometimes called sub-systems or modules), their relationships and how they are distributed.  Interface design, where you define the interfaces between system components.  Component design, where you take each system component and design how it will operate.  Database design, where you design the system data structures and how these are to be represented in a database. Chapter 2 Software Processes 21 Software validation Chapter 2 Software Processes 22 Stages of testing Chapter 2 Software Processes 23 Testing stages Chapter 2 Software Processes 24 Testing phases in a plan-driven software process Chapter 2 Software Processes 25 Software evolution Chapter 2 Software Processes 26 System evolution Chapter 2 Software Processes 27 Key points  Software processes are the activities involved in producing a software system. Software process models are abstract representations of these processes.  General process models describe the organization of software processes. Examples of these general models include the ‘waterfall’ model, incremental development, and reuse-oriented development. Chapter 2 Software Processes 28 Key points  Requirements engineering is the process of developing a software specification.  Design and implementation processes are concerned with transforming a requirements specification into an executable software system.  Software validation is the process of checking that the system conforms to its specification and that it meets the real needs of the users of the system.  Software evolution takes place when you change existing software systems to meet new requirements. The software must evolve to remain useful. Chapter 2 Software Processes 29 Chapter 2 – Software Processes Lecture 2 Chapter 2 Software Processes 30 Coping with change  Change is inevitable in all large software projects.  Business changes lead to new and changed system requirements  New technologies open up new possibilities for improving implementations  Changing platforms require application changes  Change leads to rework so the costs of change include both rework (e.g. re-analysing requirements) as well as the costs of implementing new functionality  Two ways of coping with change and changing requirements:  System prototyping  Incremental delivery Chapter 2 Software Processes 31 Reducing the costs of rework  Change avoidance, where the software process includes activities that can anticipate possible changes before significant rework is required.  For example, a prototype system may be developed to show some key features of the system to customers. They can experiment with the prototype and refine their requirements before committing to high software production cost  Change tolerance, where the process is designed so that changes can be accommodated at relatively low cost.  This normally involves some form of incremental development. Proposed changes may be implemented in increments that have not yet been developed. If this is impossible, then only a single increment (a small part of the system) may have be altered to incorporate the change. Chapter 2 Software Processes 32 Software prototyping Chapter 2 Software Processes 33 Benefits of prototyping Chapter 2 Software Processes 34 The process of prototype development Chapter 2 Software Processes 35 Prototype development  May be based on rapid prototyping languages or tools  May involve leaving some functionality out of the prototype:  Prototype should focus on areas of the product that are not well- understood;  Error checking and recovery may not be included in the prototype;  Focus on functional rather than non-functional requirements such as reliability and security Chapter 2 Software Processes 36 Throw-away prototypes Chapter 2 Software Processes 37 Incremental delivery Chapter 2 Software Processes 38 Incremental development and delivery  Incremental development  Develop the system in increments and evaluate each increment before proceeding to the development of the next increment;  Normal approach used in agile methods;  Evaluation done by user/customer.  Incremental delivery  Deploy an increment for use by end-users;  More realistic evaluation about practical use of software;  Difficult to implement for replacement systems as increments have less functionality than the system being replaced. Chapter 2 Software Processes 39 Incremental delivery Chapter 2 Software Processes 40 Incremental delivery advantages Chapter 2 Software Processes 41 Incremental delivery problems  Iterative development can also be difficult when a replacement system is being developed.  Users want all of the functionality of the old system and are often unwilling to experiment with an incomplete new system. Therefore, getting useful customer feedback is difficult.  The essence of iterative processes is that the specification is developed in conjunction with the software.  However, this conflicts with the procurement model of many organizations, where the complete system specification is part of the system development contract. Chapter 2 Software Processes 42 Boehm’s spiral model  A risk-driven software process framework (the spiral model) was proposed by Boehm.  Software process is represented as a spiral rather than as a sequence of activities with backtracking.  Each loop in the spiral represents a phase of a software process.  Spiral model combines change avoidance with change tolerance.  It assumes that changes are a result of project risks and includes explicit risk management activities to reduce these risks.  Risks are explicitly assessed and resolved throughout the process. Chapter 2 Software Processes 43 Boehm’s spiral model of the software process Chapter 2 Software Processes 44 Spiral model sectors Chapter 2 Software Processes 45 Spiral model usage  Spiral model has been very influential in helping people think about iteration in software processes and introducing the risk-driven approach to development.  In practice, however, the model is rarely used as published for practical software development. Chapter 2 Software Processes 46 The Rational Unified Process Chapter 2 Software Processes 47 Phases in the Rational Unified Process Chapter 2 Software Processes 48 RUP phases Chapter 2 Software Processes 49 RUP iteration  In-phase iteration  Each phase is iterative with results developed incrementally.  Cross-phase iteration  As shown by the loop in the RUP model, the whole set of phases may be enacted incrementally. Chapter 2 Software Processes 50 Key points  Processes should include activities to cope with change. This may involve a prototyping phase that helps avoid poor decisions on requirements and design.  Processes may be structured for iterative development and delivery so that changes may be made without disrupting the system as a whole.  The Rational Unified Process is a modern generic process model that is organized into phases (inception, elaboration, construction and transition) but separates activities (requirements, analysis and design, etc.) from these phases. Chapter 2 Software Processes 55